Mikaeus, the Unhallowed, Ashcloud Phoenix, and Phyrexian Altar

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Ashcloud Phoenix on the battlefield
• Phyrexian Altar on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Ashcloud Phoenix, adding one mana of any color
2. When Ashcloud Phoenix dies, it triggers, as well as its undying ability if it does not have a +1/+1 counter on it
3. Resolve the first trigger, returning it from your graveyard to the battlefield face-down
4. Resolve the second trigger, doing nothing
5. Activate Phyrexian Altar by sacrificing Ashcloud Phoenix, adding one mana of any color
6. When Ashcloud Phoenix dies, it triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
7. Repeat

Results

• Infinite LTB
• Infinite ETB
• Infinite colored mana
• Infinite sacrifice triggers
• Infinite death triggers